[chipsa]

Fact A and Fact B are unclassified for the XF-42. But combining Fact A and Fact B implies Fact C, which is classified. Separating each item on a different page wouldn't make the whole thing unclassified. It'd make the entire report classified. One of the facts, if not both of them, would likely be controlled information, even if unclassified, in order to reduce the likelyhood of Fact C leaking.

Example: the XF-42 has a jammer builtin. The output of the jammer is classified. But the amount of power available from the generator is unclassified, as is the percentage of power used by the jammer. Individually, either of those facts doesn't help, but together they tell you how much power the jammer has, which can help our adversaries figure out how much power they need to burn through the jamming.

That said, if any fact is classified, that by itself will make the document it's in at least that classification.

EDIT: to use your poisoning example. If it's a poison, it makes the entire thing poisoned. But there are binary poisons. Two things together make a poison, even if neither alone is (very) poisonous.